# std::optional<T>::value_or

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< cpp‎ | utility‎ | optional

template< class U > constexpr T value_or( U&& default_value ) const&; | (1) | (since C++17)
template< class U > constexpr T value_or( U&& default_value ) &&; | (2) | (since C++17)

Returns the contained value if *this has a value, otherwise returns default_value.

1) Equivalent to bool(*this) ? **this : static_cast<T>(std::forward<U>(default_value)).
2) Equivalent to bool(*this) ? std::move(**this) : static_cast<T>(std::forward<U>(default_value)).

### Parameters

default_value | - | the value to use in case *this is empty
Type requirements
- `T` must meet the requirements of CopyConstructible in order to use overload (1).
- `T` must meet the requirements of MoveConstructible in order to use overload (2).
- `U&&` must be convertible to `T`.

### Return value

The current value if *this has a value, or default_value otherwise.

### Exceptions

Any exception thrown by the selected constructor of the return value `T`.

### Example

Run this code

    #include <cstdlib>
    #include <iostream>
    #include <optional>

    std::optional<const char*> maybe_getenv(const char* n)
    {
        if (const char* x = std::getenv(n))
            return x;
        else
            return {};
    }

    int main()
    {
        std::cout << maybe_getenv("SHELL").value_or("(none)") << '\n';
        std::cout << maybe_getenv("MYPWD").value_or("(none)") << '\n';
    }

Possible output:

    /usr/bin/zsh
    (none)

### See also

value | returns the contained value (public member function)

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